System of control



3 Sheets-Shee ATTORNEY July 2s, 1925.

SYSTEM OF CONTROL Original Filed Sept, 12y

"July 28, 1925.

. R. W. MCNEILL ET AL SYSTEM OF GQNTROL original Filed Sept l2, 1921 ssheets-sheet '2 ATTORNEY W. MCNEILL SYSTEM OF CONTROL 3 Shee'tS-ShcetOriginal Filed SSD' INVFNTORS Patented any ze, i925.A

PORATION 0F IPEN N SYLVANI.

GEORG-E R. SHAY, 0F 'WILEINSBURW ELECTRIC .AND JB/IANFACTU SSTETVI i335CONTRQL.

Application led September 12, 1922.,

trol for dynamoselectric machines and it has special relation to theelectrica-l control o' a niotondriven-sliovel equipment.

One object of our intention is 'to provide a system ttor operating powershovels wherein a driving motor, of the shunt type, isconnected inseries relation with the supply generator, the control oi'E thefind-winding circuits being suoli to vary the motoraeceleratingspeed, inaccordance with the torque that is required by the shovel, andto'elllect an electrical braking action by the motor that graduallydeer' with the braking Spee t second object of our invention is toprovide a system oli the character set itortli embodying' series fieldwinding for the generator armature that differentially disposed with'respect to the Corresp(V separately excited or winding.

Another objert of our invention vide' a system of the type t variationof the generator n may serve to eliect and control erative braking ofthe motor when the shovel load overhauls the motor.

A. further object of our invention is to provide an electrical system ofthe aboveindicated character, together with 'a eontroller for governingthe operation of the machines, whereby electrical braking of the motormay be selectively v.eleetefl by varying the generator Voltage with thecontroller in a position corresponding to drivinr the load, or by the.shovel load, overhau'ling the motor when the Controller occupies itsofi position.

Still another object of to provide e sy) motor and switch shunt type oliis to 'pro vili erom inventiy in embodying a nig means for Serial No.@$937, llfenewe lieceinber i8, 132e.

the direction ol' operation thercoit', to with an arrangement o relaydevie anc, "55 a controller to prevent the closure one set of switching;ineens after the other has been elf Vd, until the )Jolt-age of 'themotor decrees s to a predetermined value, corresiLn/ndin;` to nrelatively low sneed. T JL further object or our invention is to providerelay device Yto: governing' the excitation oi' llie motor iieldwinding', the relay device being prfnf'nled with two aetueting; coils,whereby, upon the de-energi aetion of one'yeoil by movement ei'f thecontroller to off pi, bieri, a second coil. is Connected across themotor armature,

.serves to .maintain the excitation. el the rence with our presentinvent forni o; i is e enrve criant ly ii eating' the operatingciieraotsiistics o shovel-driving motor under ve l "is, including twodii. of eleltrical lorelllingA liefe ring to Figure l of l; dra-wing,'the power shovel here showi:` comprises CeliI 1,whicli rotatably nienupon a. suit- -i hearings 3, a

the aninliarv e f our svsten 3 l able base 2 by mea-ns of 1' pluralityof trucks being mounted beneath the base 2 to permit operation of tineshovel upon the usan? trecl rails i swinging boom S, a suitable flipper7 end ,a clipper erin S, which extends to enintermediate point of theboom, are arranged in a familier manner.

The cab i encloses a mejor portion of electrical equipment fortransmitting energy to the desired parte et the shovel equipment toproduce the loisti'g, thrnstf and swinging .mentions` generator set.

tire

enife li moan the of the cali remote it and may conveniently .en i

in. ripper 165 drive CIV.

ener qnel circuit, and e suitable number of diea-blcs 14C and the boomWheel 15, to the dipsynchronous motor that is supplied with gy, in theusuel manner, from en exterrect-current generators, one of which Will'be specifically described in connection. with Fig. 2.

The electric driving apparatus 12 for providing the hoisting motion ofthe clipper is located in an intermediate compartment of the cab andpreferably comprises s plurality of similar direct-current motor, whichwill also loe specifically described in connection with Fig. 2. Theusual set of gear- W'tieels and hoisting drums 13 is provided inconnection with the driving appara-tus l2 to transmit energy, throughthe customary per 7, whereby the flipper may be raised and loweredaround the' intermediate point of mounting on the boom 5, as desired.

Ilie thrust motion oic the clipper is gov-- erned by en electric drivingzippers-tus 17, Wiiicli preferabiy consists oiifou single motor drivingsuit-cible gear-wheels for engaging a. rack surface upon, the dipper Sl,1n accordance with the usuel orectice.

The swinging motion or the celo is controlled by ineens of electricaldriving epperstus 18, which may comprise e single motor that is suitablyconnected, through bevel gearing, to drive the celo 1 ro'atebly with.re-

spect to the base 2 through' the agency oi' the roller bearings 3.

"liie system to 'ce described in connection with Fig. 2 relatesspeeilicelly to the hoist ing or digging motion of the dipper 'i'.However, it Will be understood tlist the operation of the swing and the'thrust machinery will be of the seme general type as regarnisscceleratiim or application of power.

v In view of this general similarity, it is not deemed necessary to'refer in det'f-il to the control systems Jor the thrust drivingapperiitus if? and. the swing driving apparatus 1S.

Rerring to i E?, the system l'iere shown comprises a direct-currentgenerator 101, constituting part of the motor-generator set 11, forsupplying energy to a. pair of seriesconnected shovel-operating motors102 and 103, which together constitute tlie hoisting driving apparatus1Q. An auxiliary generator or exciter 104, which preferably coustitutesone element oi the motor-generator set 11, is employed for exciting;rthe genen etor iOl and tile driving motors, a resistor 105, which muylie adjusted liv means of c. pluraiity of switches 10G to 109,inclusive, being 'iuded in circuit with the exciter. A reversibleniulti-positicm controller 11() is provided for governing@I theoperation of the supply generator and the driving motors during" botlithe accelerating; and. the regenerative periods.

A, olrslity of sets of direction-governing switc es 111 end 1&3, and 112end 111i, re-

meneer spectively, are provided Jior controlling the direction ofenergizetion of the seperately excited or shunt type ofi-field winding124 for' the generator 101, thereby governing the direction ofoperation' of the shoveldriving motors, as subsequently more fullydescribed. A plurality o1 relay devices 115 to 121, inclusive, areprovided for 'automatically governingT tlie relative operations or' thesets of direction-controlling switches and of e switching device that isadapt ed. to very the excitation of the driving motors 102 and 1053,hereinafter more vfully explained.

'.iiie supply generator 101, in addition to the shunt type offield-Winding 12e, coinprises 2. suitable commutator-type armature 125and e series fieldivinding 1:26, which is differentially disposed withrespect to the iield Winding 12e. The armature 125 end the fieid Winding7126 are connected in di rect .series relation, that is, in e closedloop with the cornmuistor-tj/pe arrnatur s l2? and 128 of the drivingmotors, to insure equsi 1ivision of ioctl between the nieto-rs. The

'eiieretor 101 is preferably of the familier ree-wire type, set ofbalancing coils 1.29

:zi-*ing common 'terminal grounded, their orlier tei-minnie beingconnected through suiteoie brush as to slip rings 130 on the renerstorarmature 125. ln this wey, the potential; to ground from any point oneither oi! the two motors is iiniiiedto one-hair" ci the genere-torvoltage,

/l'fherees, the supply generator 101 is 'rims of the diiierenticllycompound-Wound type,

the dri'qing 102 and i023 are excited solelj7 by shunt-type fieldwindings 131 and 1532, respectively, which may be connected in seriesrelation with e suitable resistor i553 across the terminals oi theexciter 104.

Equal division of leed between 'iie motors is further insured. oy theseries relation of the field windings and The exciter 104': coinprisesecommutatoriype arineturefll: and e shunt i'ieil Windn ing; 135, which isconnected, through a verialole resistor 131i, across the terminals ofthe armature 134.

The controller i shown as provided with an intermediate o'l position andtwo operative positions a to e, inclusive, and a to e', ineiusive, thatrespectively correspond io forward and reverse direction of t indiczitedthe shovel-driving motors, as by the corresponding legends Thecontroller 11() comprises :i plurality of control finger-s ifi-0 to 146,inclusive, weich ere adapted to engage suitably contion o thecontroiier. The sit-ive termiiA ictA i is

posilie. inteilovk 75 ie relay 1l t1 P is t f the b @mbv s of 110i" 90the i age of the 'lo piedeter @matin G" 5 is on, irrespecicn lll to 1Lis entac on of e Closure is Con- 1 6i, ne frei 146 o the ie- 105Wii'idins' Rotors, Wli

e wavy mug gli the onductor :elim

motor s closed con @tor er izatio becomes d 166 to humus u iis relayicl1-de l the' a Coil 162 for acl n *all m the thi* 5 bhe an wing.

to il;

ne. i

tors lative Held l. s, one of lOf lli?. lle drivin .i

0S (if incl urlin the dr ct sli a Cncu in i um occurs as; soon as lvmgative ondu t the en si'nllcient 'to a il is connected across u.ointcuniu 16 uctol' 157 that the rela relation to cluctors .l

,ill losed 1' Control conductor T 0 the ne yhe ncl tha Y drm'Q.inaiutains t s re f is att con ions

.negative Concl nus u onductoi l 0f the rela K t open he rela me a sconda [lll mmm

two co vircui md. v0.

Hillel 1'! quen 2.o, conti@ 'Wili )AL IL l? w ls of bers l it

anu if in th 32 of oils @lay ll my :armina ized, and t ic me of subs@ itl sitioli,

L liu swim-l1 l PP position he tively enel tha .lt W

yLed 1n h 71T-aii' ivirig motors l issi- ,ne o il mit fi? a all' Oulu@rela de eslled i0 a l* :aliased as are G lier init comme@ nil-opel:

cli'

o anadur to im 430m' Pl aereas the ne lons coil cir 1' l1?j the negativeemes-s .El ll L luis penny lf l conducen' ,i 1

cha-t 10.1 of 'the con @ce ,Tela "'f une lira-,lich i ger 147? meexciter y de negat migas 0 S H n minal of cond met man low lav

lle

l posi l l 14.8 to pmrne switches U5 Way, the reexciudecl from theinding 124, asm

1i, inclusiv@7 'met segment ze mtl Close Ve. ln this' graduallyeratoylelcl w to l the con een/argl L ii'zclusi he gen if) toit :igorscl accordanca upp @www vol ing sul

tures l of yi Siracl ect eversed @vel nOt01S file Conto its position eitolie; Gf the other diretio11- nfl 114 until the,

ff aleczeased preventing in- `ppie (le lie Conf/rolling sw and@ seriesheld vvo1.' comas int the C of 'il' @reni-ly hy reason' mf it ly tracedcircuit through the conta-ict 1neni` bers thereof. and. tlie actuatingcoil of -relfny 11G is again completed to effect the v el.

closure o1l Jdie rosy 116. The openin 'the relay 'll-5 n o effects the(le-enen tion of the sctnn'mg coil ci the reis);

thus causing i-lie opening' thereof. 'lll' lays 115 ond 11i src thusreturned to el normalpositions und, ss soon lire ie 11: occupies itsoppor or closed position, nenT circuit is esi'nblislic-il from theconiact segment 149 of tire controller 11C- glirougli control finger14:1, comluctor 170, Contact members of the relay 115, conductor ll'lund direction-controllino swisclies 112 and to the neg'itive conductor15'?.

to the critical value, :L circi'iit The direction of energization ol the1n crater ield Winding 12e is tlxus rever-1: accordance with 'well-knownnrinc whereby the direction oi' energrimi'ir'ni oli toc motor armatures127 ond )QS is also ifo-- Vers-ed.

fis soon :is the rnotor milf-.ge hes increased csialilislied troniconfluclm 163 through the actuating coil of relay 118, eonductor 172,intenlock or auxiliury contact niemlor tlio switch 112,' in iis closedposition, nud wonductors 17317-i und 166 lo the opposiie side rtl-iedriving motors. "lllie relay 'le is time raised to its upper position tocomplete o circuit from the positively energized doctor 156 tln'ougl'itlie Uontnel members of tlie relay 118 zin/. the octunfii coil or lierelay 120 to the negsiive ec-ndictor 157'.

The relay 1Q() serres to ln'idffje the interlock on illedirection-controlling Witch 112 bydiroctly joining one terminal s of thecoil. of tlm relay 11S to conductor 174.' 'in this wey, the relay 118 ismaintained closed, irf respectivo of subsequentopeningr oi thediroetfin-controlling switch 112.

Otherwise, the ope rtion o'fvtlie 's 'stein is tlic sinne ais tlnltprcviourl described, since the contact segment 119 ot the con* trolierllll corresimnds, in form, to 'the conniet segment .148. A Y

it will lie a ppreciutedWithout detailed de? s'cription tlnit, in cesethe controller 110 is stddenly actnuted from a. reverse to s for werdposition, the set of relay devices 11S, 11E? and '19() operate in thesuine. In nner the relays 115, 116 ond 117 te 'prevent the closure olthe direetioncontrolling switches 111 and 113 the Voltage wereleft-,connected permanently acrossthe exciter 1011 to receive the fullVoltagethere'- ol?. However', suoli reduction in the 'field energizetiondoes not coeur until the volt-- of the moin niorors lies dropped to a cvalue, thereby insuring full field encrgizcnt on during the deceleretingperiod.

This result -isob'teined by reason of the :action of the twonetnetingcoils 161 and of lie relay 121. Although the jointI ect-ion of the twocoils Wes employed to close the rfc-ley und maintain .it closed, aspreviously described, tlie winding' 162, which is connected across theterminals oi' the main motors, .adapted to alone maintain the relay inits closed position, in accordance lr iifunilier principles,Consequently, slrlioug'li the coil 161 becomes ie-energized when thecontroller is thrown to its oil position, the eley 121 does not openuntil the voltage oir tile main motors decreases to u rcdeterxninedvelue. At that time, therefore, the actuating coil oi the switch 122becomes dni-energized to allow the reinsei-tion of the resistor 133 in.circuit with the shunt-type field windings4 131 and v132 el' thedriving' motors, to decrease the heatthereof.

Arleqn-neintion may be selectively effected by either one ol'two methods'Without em pinyin@ any resistors to absorb power. In fixe {irst pince,it is desired to lower the lefulnfter the controller has been actuatedto irs full 'forward-running or hoisting position c, 1For exemple, illecontroller 110 may 'be actuated tois oil osition'to stop the motorsund., upon application of the mechanonl brakes, tl loud will. be held inits elefued position.

For lowering; under the control o the operator, the controller' 110 maybe first so' tusted to its initial reverse or lowering position a',whereupon the desired reversal of4 voltage of the main motor armatures127 and 12S will occ ir in the manner .previously described.' Thenecessary starting or kickoil fiction time obtained. However, ifdesired, the controller may be actuated to any of' its reverse positionsa to e', inclusive, to provide s corresponding dierence in tile rete orretardation, the position e affording 'the highest brakingvrste.

The characteristics of the generator and motor armatures' in the closedmain circuit, including the diierential action of the series fieldwinding for the supply generator, are suoli to prevent undue' surges ofcurrent mev i Leanser during the braking period, and, moreover, tonormally maintain the voltage of the motors, which are now driven asgenerators hy the descending load ol" soil, or other material, slightlyabove that of the generator.

The rate oiZ retardation may he varied within relatively wide limits bymanipulathe controller to other positions on the lowering, side. asdesired. ln this way, the generator lOl is driven a motor to returnenergy to thesupply circuit through its norn'ially driving machine andthus et feet true regenerative braking of the equip*- rnent.

The load mav he safely lowered by means of the electrical braking justdescribed, or, if desired, the following method may he einployed:Assuming that the controller again occupies its forward running positione, upon releasing the mechanical brakes und actuating the controller Vtoits ol' position, the descending load will gradually overhaul the motor,which will exert the well-known electrical braking or regenerating,7action that such operation. causes. The braking effort may he 4regulatedin this case hy variahly energizing the generator Field winding in thedirection corresponding to hoisting, will he readily understood.

By reason of the employment of the shunt criving motors 102 and '103,therefore, the operator may choose between the two different types ofelectrical braking, whereas, il a series driving motor were employed,only the latter, or overhauling braking action, would be possible.

The previously described operations of the main driving iriotors aregraphically indicated hy the curvescf Fig. The curves marked Horsepower, Torque, Vo ts and Motor l). lil. inthe First quadrant of thecurve chart are or" a familiar character setting' forth the operatingcharacteristics oli the' shunt motor. From these curves it will he seenthat, although. the shunt motor, in general, is a constantspeed machine,nevertheless,"the accelerating speed of the driving motors will not hegoverned solely hy the variation of supply- ;renerator voltage, hut thespeed will also vary in accordance with the torque that is required bythe shovel throughout its complete hoisting operation. In addition, thecharacteristics ot thegenerator are e fidently such that it '.villf`heimpossible to overload the motors or overstress the hoorn.

Furthermore, regenerative braking of the first type set forth above,that is, weaken-- ing the generator field excitation in such manner asto maintain the generator voltage below 'the voltage of the load-drivenmotors, is indicated hy the curves iii-the second quadrant of the curvechart. Curve A represents motor R. l. M. for given exciting saidcondition of the generator excitation by 'means of the shunt-type fieldwinding 124 and a relatively low motor excitation by means of theshunt-type held windings 131 and 132-. Curves B and C indica-'te motoroperation for similar generator excitation and `gradually 'increasingmotor excitation. Curve D represents the regenerative voltage. Fromthese .urves it will he noted that the electrical action of the shovelmotors gradually decreases with the lira-king speed.

It the second type of electrical braking,r is desired, namely, thatcaused by the overhauling action of the loaded shovel, the curves shownin the fourth quadrant of the chart apply. These curves are labeled A',B", C and D and respectively correspond to the previously indentiiedcurves A, B, C- and Consequently, 1oy reason of the employment of adriving motor of the shunt type, electrical braking thereof underconditions of lowering a loaded shovel may be effected .at will,according to either the second quadrant orthe fourth quadrant set ofcurves thatare illustrated in Fig. 3, whereas, in the case of a seriesdriving motor, second quadrant operation is impossible by reason of thedifierent speed-torque characteristics of the. machines. Y

We do not Wish to'he restricted to the specific structural details,circuit connections, or arrangement of parts hereinI set forth, asvarious modifications thereof may he made without departing from thespirit and scope of our invention. Ne desire.

therefore, that only such limitations shallf. 'A

he claims.

We claim as our invention: l l. The combination with a power shovel.,

of driving' means therefor" comprising'a genimposed as are indicated inthe appended'1 erator and a motor armauire connected iir' seriesrelation, vmeans for operatively'con- .sorting said motor armature tosaid shovel, a ser es and a shunt-type .iield winding for generatorarmature, a second shunt-type eld winding for alone exciting said motorarmatureand means comprising sai-d seri-es field winding for varyingthe, effective excitation of said shunt-type field windings to vary themotor accelerating speed in accordance with the torque required by theshovel and to efect an electrical brakingr action by said motor thatgradually decreases with the bra-king speed.

2, The combination with a power shovel, of driving mea-ns thereforcomprising a compound Wound generator and a plurality of motor armaturesconnected in series relation, means for operatively connecting saidmotor armatures to said shovel, a plurality of shunt-type tieldfwindingsfor respectively alone exciting the "motor armatures and means'.tor'vaiying the excitation of at least one of said shunt-type fieldwindings as the eiective excitation of said. generator changes to varythe accelerating speed oi tlie motors in aocordancewitli tlie torquerequired by tlie shovel and to effect an electrical braking elution bysaid motors that gradually decreases with the braking speed.

3, 'lilie combination Witli a power shovel, of driving means thereforcomprising a. gencrater and a plurality of motor armatures connected. inseries relation, ineens for op" erstively connecting said motorarmatures to scidgsbovel, shunt-'ty e and e diil'erentially Wound seriesiield i iiiding for exciting said generator orinuture, ri `plurality ofsliiint-type field windings for respectively alone exciting tlic inotcrarmatures andk 'ineens including aii exciter and said seri s fieldwiiidinff ici' varying the eectiveexcitation o tie generator shunt-'typefield Winding to vary the accelerating speed oi'f tlie motors inaccordance with tbe torque required by tlie shovel and to effect anelectrical braking action by' said motors.

4. The combination with apen/er shovel and a motor armature operativelyconnected tliei'eto,`oi" a generator armature electrically connectedtosaid motor armature, sliunt type field windings toi-respectivelyexciting said armatures. a.' series iield Winding for tlie Generatorarliiature and ineens for Sfr ' under electrical braking conditi varyingthe voltage impressed upon the motor armature by adjusting excitation ofcertain of said iield windings for goverin ing,` the speed of 'the motorarmature under accelerating conditions and. for governing the currenttraversing seid nieto armature 5. The combination with a power shoveland aA glura'lity of motor armatures opere-fr tively vconnected tbereto,o :i generator armature connected yin series relation with motorarmatures, 'shunt-type iield Windings for respectivelyexcitingf seidorina tures, si differentially Wound series ield Winding for thegenerator armature and means for varying the voltage impressed upon tbemotor armatures by adjusting the excitation' of the generator fieldwindings .for governing the speed of tlie motor arma.-

' tures under accelerating" conditions and for governing the currenttraversing' said motor armatures under electrical. braking conditions.

6. The combination with a power shovel sind a plurality of motorarmatures opera,- tively connected thereto, oi a generator armatureconnected in series relation with said motor armatures, shunt-type lieldwindings for respectively exciting seid armatures, and a: series fieldWinding for said generator air mature dii'ierentially disposed withresiiec to thecorreegonding shunt-type lield 'windilie combination witho power shovel noemer tion with said motor ernia-tures, series re` latedshunt-type lield windings-'forlrespectively alone exciting said motorarmatures, and differentially related sliiint-type and series fieldwindings for exciting said genen ator armature.

8. The combination with a power shovel and a motor armature operativelyconnected thereto, of a compound Wound generator having an armatureelectrically connected to said motor armature, a shunt-type fieldWinding for alone exciting seid motor orinature, and means forcontrolling the eliective generator field excitation wherebyregenerative braking of the .motor may be effected when the shovel loadoverhauls the'iiiotcr.

9. llie combination with a power shovel and motor armature operativelyconnected thereto, oi e compound Wound generator -hiiviiu an armature.electrically connected to sai i motor armature, a shunt-'type eld'winding for alone exciting said motor arronture, and a reversiblecontroller for varying the "effective generator ield excitation tomaintain the generator voltage below thev voltage generated by the motorunder shovel-l-oad-lowering conditions, whereby regenerative brel-:ingof the motor maybe effected when tliesliovel load overliaiils 'themotor.

l0. The combination with a. power sliovel and a plurality of 'motorarmatures operetively connected thereto, of a di'erentially compoundWound generator lieviti-Jg an arma# ture connected in seriesrelationiwitli said motor armatures, a plurality series-re latedsliuntlype field windings A`for respec armature, and a controller `itergoverningthe operation of the inacliines, andmeans where-y byAelectrical `braking of the" inotor may be selectively Veffected li'yvarying 'l'zlie'feifectiize generator voltage with the controller inapostifgn corresponding to driving-tl'ieloed or o sliovel loadoverlieuing the 'motor Wlie i the controller occupies its o5 'gesitionl2. The coiiibinetion with power ehotel und noter ermatureoosretivelyconnected lll) sliovel-lod-loworin# coniii'tins with ninemsn i DV@ziniflnf. plurality of motor armatures ener-- iwely connected ihereo,o'fn coinpoiind oi'infl generator having nn armature '.neciecl in seriesrelation with said nioor z`i`rmzit-nres, o plurality of series-relatedshunt-type field windings for respectively nlone exciting saidY motorarmatures. nnfl reversible controller for governing' the ogierntion ofsaid machines, and ineens Whereby eleccricnl braking of the motors inffbe selectively effected by varying tho effective genernlior fieldexcitation to maintain the generator voltage below the combined ifoitagegenerated by the motors under shovel loncl-lowering conditions rfi'zhthe conrioller in an operative position or by the shovel loadoverhanling' lie motor when the con troller occupies its oil iosition14. In e system of control, ilie coi" tion with n driving motor sv lilia' means for governing the ilirection. o'i ation o!" sind motor, of eplurality of nor melly energizefi swiizches cocreepenclin' v 1' w WM.the respective ohci oi, inc-loi climatico.,

a.v conrollcr for .eifcriing lie close: or' zi selected set` orsvxiiciiingg' ineens. iclnj! having' :i coil innerenpon connected aero,seid motor, nml ineens for preventing ine closure of another sei of saidswiiciiing ineens {nni said relay drops 'io its lowvoltzige position.

l5. ln :i system or" control, the combina,- tion with n driving motorand svi-'itching' ineens for governing the `direction of opor- :ition ofsaid motor, of :i plurality of nermally energizecl'relnys corresponding!to 'ihe respect-ive directions of motor operation, :iv controller foreffecting the closure of a selectecl set of said switching meansihroiigli one of said relays, another relay having n. coil thereuloonconnected across sai nioicr ine-ans governed by S21-icl Telef; for estnliliff'hing :i1 holding circuit therefor independent o'scicl set ofswitching ineens, and ineens for preventing the closure of another setof said switching means' nii'lzil seid oher relay clrops to itslori-voltage position.

i6. In a system of conflrol, the combinet-ion with n driing inoor and aplurality o'l s clays corresponding; io

respccire clirecions of motor operiii l le controller 'for effectingizhe closure o selecicfl pair of seid swiches through of scifi releys,o, iiird relay having n @use said inoror by iin inici:

i u govcrnecv die operation of said coil :For bridging sul iniberloclrand for ellecting' the opening oi die remaining normally energizer;relay, Where/bj.' the operziion of the controller to ai reverse-dposition is ineffective fro close the remaining' pair of .said switchesnnil siii-.l iiiirci relay drops to its low-roly infie position ioper-init. ilie ionrth relay to open and therein7 effect the re-energ al'tion of said remaining normally energizedrelaja l?. ln zi systeni ofcontrol, the conibination with a, driving moo-i' having an orina* tn ieend n lielcl Winding', of means for inedifying" the eii'eciire iiiiX ofthe lieldwinding, :i plnrl coil relay for governing said modifyingmeans'and lia-ving one coil-connected across the motor armature, and acontroller for governing another coil to effect operation of snifimodifying Ine-ans by the ioint nciiion of said coils, whereby upon thecle: b'izn'ion of one coil by inorenien or" che controller to ofiposition, lie coil connecteri across like motor nrnifitnre serves to inmin die conciiion of said modifying inc until "che r weinige decreasesne.

erg-wien si' i :nimh coil onnncioss the ino-ier, line sole accion or orc necesenry to A *l ne relay lon: action of the lnsl ierneil; coil alonebeing;

snlicient ro hohl the relay close, Wlicrebi7` sind coil serv fo maintainthe normal opcreiingf condition of said resisiornnfil iflie motorvoltage flecrenses io si jecleterminel vaine.

in slsein of control. che combine with rlriring; inotorhsrinp; an orma`ture :iii-i. e field Winning, of a resistor in series relacion with seidfield Winding n normally open switch connected 'lo ihe *Lerininals 'o'said resistor, n plural-coil relay 'for goi/'emin'g scifi switch :inclhaving; one coil connected across the motor armatore, nifl coni'rollerier governing nnother coil in ci'iecb Closure of said' swift-cli by n' esolo aiioii of saicl other coil,k wiierelayion che iie-cnergizntion ofone coil hy 'inoveinen o the contr ller off position, lie coil connec'l'efl across the motor armature serves to I seid switches, n fourthremaintain said switch closed to short-circuit said'resistor until themotor voltage dew creases to a predetermined value.

20. In a system of control, the combination with a dynamo-electricmachine one. means for governing the direction ot operation thereof,A'of a plurality ci normally. energized switches corresponding to therespective direction of machine operation, means for eectingtheoperationot "a selected portion of said governing means, and meansfor preventing the operation of another portion of said overning meansuntil a predetermined mac ine voltage obtains.

21. `The combination with a. power shovel, of driving means thereforcomprising a gerr 'erator and amotor .armature connected inSeriesreIatiOn, meansfor operatively' connecting said motor armature tosaid shovel,

afseries and a-shunt-t'ype eld Winding for exciting said generatorarmature, a. eid Winding for alone exciting saidxnotor armature andmeans .comprising said series field Winding for varying the 'eleetiveexcitation of said field windings to Ay'ary the motor ae celex-atingspeed in accordance With the ltorque required bythe shovel and to eectan electrical braking action by said motor that gradually decreases withthe braking Speed# f '22. The combination with a power shovel, ofdriving means therefor comprising a genn erator and a plurality of motorarmatures connected vin series relation, means for oper ativelyconnecting'. said motor armatures to Said shovel, a shunttype and adiE'ere-ntially ,w'ound series ieldiwlnding lfor exciting said'generator armature, and means including an exciter and said seriesjeld`Winding tor yarying,the eective excitation of theagenerator shunt-typefield 'vrind-ingtov yarytthe accelerating speed of the -motors'inlaccordance with the torque requiredliy `'the shovel aiidlto'eiect anelectrical braking action. Aby

said motors.

23. Thetcoinbination With a power shovel and a motor armatureoperatively' connected thereto, of a' generator arma-ture electricallyconnected to said motor armature, field Winding-s forvrespectivelyexciting said armatures,

a ,series field winding for the generator arma- `l`ture, and means forvarying the voltage iinressed upon the motor armature by adjust-A"'vindin'gs yforgoverning the speed of the' "'niotor armature underaccelerating conditions and for governing thelcurrent traversing saidmotor armatureV under electrical braking conditions.

meneer ditions and for governing the' current traversj said motorarmature under electrical braking conditions.

rl`fhe combination with apower shovel plurality ci motor armatures`operatively connected thereto, of a generator ar mature connected invseries relation with said A motor armatures, main ieid windings forrespectively exciting said armatures, ,and a t'ield Winding for saidgenerator armature diterentially disposed with respect'to thecorresponding main field Winding.

26. The combination with a power shovelv and a motor armatureoperatively connected thereto, o'l" a compound Wound generator having anarmature electrically Vconnected to said motor armature, a shnntetypefield Winding 'for exciting said motor armature, means for controllingthe effective gen crater field excitation whereby regenerative brakingof the motor may be effected when said motor is plugged.

. 27. 'lhe combination with a power shovel 'and a motor armatureoperatively connected thereto, of a compound. Wound generator haring anarmature electrically connected-- to said motor armature, a shunt-typefield winding for alone exciting said motor arina-- ture, and areversible controller for varying the eective generator field excitationand means co-operating l'with said controller for limiting the currentoic regeneration when said generator excitation is suddenly reu versed.

28; The combination with a power shovel and a motor armature operativelyconnected thereto, of a compound 'wound generator g an armature'electrically connected to' .said-motor armature, shunttype field Windingtor alone exciting said motor armahaving ture, and a reversiblecontroller 'for varying the effective generator field excitation andmeans rendered effective when said controller is abruptly Areversed forlimiting the current of regeneration;

Intestimony whereof, we have hereunto subscribed our names this thday of[iepu tomber, 1921.V

nALrn: iv. MCNEILL. stoner. e. sean?.

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